Spatial thermal density reduction for MMWAVE antenna arrays

ABSTRACT

An apparatus, method and computer readable medium for special thermal density reduction by antenna thinning. A system comprises N transmit/receive (TX/RX) chains, where each TX/RX chain comprises an RFFE and each RFFE comprises one or more thermal sensors configured to measure heat in the RFFE. An antenna array coupled to the plurality of TX/RX chains. A codebook that comprises a plurality of code words configured to respond to real-time heat measurements from the thermal sensors in each TX/RX chain is configured to switch off selected TX/RX chains to reduce thermal density at the antenna array while maintaining M RFFEs switched on, where M&lt;N and the desired beamforming gain is 10 log 10(M).

This application is a U.S. National Stage filing of InternationalApplication No. PCT/US2018/040441, filed Jun. 29, 2018, titled “SpatialThermal Density Reduction for MMWAVE Antenna Arrays”, which isincorporated herein by reference in its entirety.

TECHNICAL FIELD

Some aspects of the present disclosure pertain to thermal management ofRF-front end components in wireless communication systems operating atmillimeter wave (mmWave) in frequencies.

BACKGROUND

The fifth generation (5G) or fifth generation plus (5G+) is envisionedto support enhanced vehicle to everything (V2X) systems. V2X systemsrequire vehicle platooning advanced driving (e.g., fully automateddriving), extended sensors, and remote driving. In addition, drones arebecoming one of the emerging technologies for remote operation, realtime sensing and reporting (e.g., video delivery). All theseapplications may need high data rates, low latency, and highreliability. For example, vehicle platooning may need periodic dataexchange between cars for platooning operations, which requires lessthan 3 millisecond (ms) end-to-end latency for cooperation andcoordination. For advanced and remote driving each vehicle may needdata, from sensors, of their nearby vehicles for coordination to enablesafer travelling collision avoidance, and improved traffic efficiency.In addition, to enhance perception of environment, the exchange of rawdata from local cameras, light detection and radar (LIDAR), otherradars, road side units and servers are needed. Therefore, high datarates with very low latency and high reliability may be needed forautonomous vehicles and drones. As examples, extended sensors and remotedriving requires 99.99% and 99.999% reliability, respectively, andsensor information sharing between vehicles supporting V2X applicationis believed to require 1 gigabit-per-second (Gbps) data rate. Similarly,drones require very low latency for coordinating with other drones. Forthe above applications, communication systems which can support thestrict requirements given above are needed.

There are some standard developments for the system applicationsrequirements discussed above. These include dedicated short rangecommunications (DSRC). However, DSRC can provide data rates up to 27megabits-per-second (Mbps). Further, the 6 GHz bands (e.g., long termevolution (LTE) and other current systems) are already congested andhave limited data capacity. As a solution, then, the large spectrum ofmillimeter bands can be considered for high data rate communications. Inaddition, mmWave beamforming provides inherent increased locationaccuracy, inherent physical layer security, and extended coverage.However, high frequency operation at mmWave frequencies will generateconsiderable excessive heat energy due to operation of the circuitry ofthe radio frequency front end (RFFE). Because power efficiency of RFcomponents decreases as heat energy increases, a critical issue withmmWave systems is thermal management of RF-front end components. Henceimproved thermal management at mmWave frequencies is needed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a mmWave system, according to some aspects of thepresent disclosure.

FIG. 2 illustrates a user device, according to some aspects of thepresent disclosure.

FIG. 3 illustrates a base station radio head, according to some aspectsof the present disclosure.

FIG. 4A illustrates a radio front end circuitry (RFEM), according tosome aspects of the present disclosure.

FIG. 4B illustrates another RFEM, according to some aspects of thepresent disclosure.

FIG. 4C illustrates an example of a system for generating multicarrierbaseband signals for transmission, according to some aspects of thepresent disclosure

FIG. 5 illustrates a multi-protocol baseband processor, according tosome aspects of the present disclosure.

FIG. 6A illustrates a periodic radio frame structure, according to someaspects of the present disclosure.

FIG. 6B illustrates a periodic radio frame structure using frequencydivision duplexing (FDD), according to some aspects of the presentdisclosure.

FIG. 6C illustrates a periodic radio frame structure, according to someaspects of the present disclosure.

FIG. 7A illustrates a constellation design of a singe carrier modulationscheme containing two points, known as binary phase shift keying BPSK,according to some aspects of the present disclosure.

FIG. 7B illustrates a constellation design of a single carriermodulation scheme containing 4 points, known as quadrature phase shiftkeying (QPSK), according to some aspects of the present disclosure.

FIG. 7C illustrates a constellation design of a single carriermodulation scheme containing 16 points, known as quadrature amplitudemodulation, according to some aspects of the present disclosure.

FIGS. 8A and 8B illustrate examples of alternate constellation designsof a single carrier modulation scheme that may be transmitted andreceived, according to some aspects of the present disclosure.

FIG. 9 illustrates an antenna array system with smart radio frequencyfront end (RFFE) selection sequence to distribute heat over the antennaarray, according to some aspects of the present disclosure.

FIG. 9A is a diagram of hardware configured to measure temperature atone more locations within each radio frequency integrated circuit(RFIC), according to some aspects of the present disclosure.

FIG. 10 illustrates a uniform linear antenna array with ten antennaelements.

FIG. 10A illustrates subarray selection and codebook antenna thinningaccording to some aspects of the present disclosure.

FIG. 11 illustrates an example of TX/RX selection for thermal density,according to some aspects of the present disclosure.

FIG. 12 illustrates comparison of the array patterns of an antenna arrayusing the disclosed thermal mitigation with subarray type TX/RX chainselection, according to some aspects of the present disclosure.

FIG. 13 illustrates a comparison of side lobe levels (SLL) withsimulated antenna array operation in accordance with the presentdisclosure, and SLL of simple sub-antenna array type operation,according to some aspects of the present disclosure.

FIG. 14 illustrates a comparison of antenna array gin as a function ofazimuth when all antennas are operated, and antenna array in when theantenna array is operated in accordance with the disclosed thermalmitigation, according to some aspects of the present disclosure.

FIG. 15 is a flow chart that illustrates a method, according to someaspects of the present disclosure.

FIG. 16 is a block diagram of an example machine upon which any one ormore of the techniques or methodologies discussed herein may beperformed, or in which apparatus discussed herein may be incorporated orused, according to some aspects of the present disclosure.

DETAILED DESCRIPTION

The following description and the drawings sufficiently illustratespecific aspects of the present disclosure to enable those skilled inthe art to practice them. Other aspects may incorporate structural,logical, electrical, process, and other changes. Portions and featuresof some aspects of the present disclosure may be included in, orsubstituted for, those of other aspects. Aspects of the disclosure setforth in the claims encompass all available equivalents of those claims.

The millimeter wave frequency range, where the disclosed systems arescheduled to operate, is formally defined as a frequency range spanningabout GHz to about 300 GHz, and in practice currently covers severaldiscrete licensed and unlicensed frequency bands.

The only unlicensed mmWave frequency band currently available is in thevicinity of 60 GHz. Licensed frequency bands are likely to include 28GHz, 39 GHz, 73 GHz and 120 GHz. The availability of these bands and thespecific frequency range of each varies by regulatory jurisdiction, andin some cases (specifically for licensed band operation) there is stillsignificant uncertainty as to regulations in some countries. Challengesassociated with mmWave-based cellular communications include limitedrange, directionality of antennas of the rang, signal loss because ofuse of regular cables instead of traces, and challenges with integratingmultiple antennas for beamforming. These challenges are addressed asdiscussed below, and may include use of polarization innovations, traceand other line use to avoid signal loss, and an improved ability for usein beamforming

FIG. 1 illustrates an mmWave system 100. The system includes twocomponents: a baseband circuitry 101 and one or more RFEMs 102. The RFEMis connected to the baseband circuitry by a single coaxial cable 130,which supplies a modulated intermediate frequency (IF) signal, DC power,clocking signals and control signals. Applications of mmWave technologycan include, for example, WiGig and future 5G, but the mmWave technologycan be applicable to a variety of telecommunications systems. The mmWavetechnology can be especially attractive for short-rangtelecommunications systems. WiGig devices operate in the unlicensed 60GHz band, whereas 5G mmWave is expected to operate initially in thelicensed 28 GHz and 39 GHz bands. A block diagram of the baseband 101and RFEM 102 in an mmWave system is shown in FIG. 1. The baseband 101 isnot shown in its entirety, but rather shows an implementation of analogfront end. This includes a transmitter (TX) 131 a section with anupconverter 103 to intermediate frequency (IF) (around 10 GHz in currentimplementations), a receiver (RX) section 131 b with downconversion 105from IF to baseband, control and multiplexing circuitry including acombiner to multiplex/demultiplex transmit and receive signals onto asingle cable 130. In addition, power tee circuitry 109 (which includesdiscrete components) is included on the baseband circuit board toprovide DC power for the RFEM 102. In some aspects of the presentdisclosure, the combination of the TX section and RX section may bereferred to as a transceiver to which may be coupled one or moreantennas or antenna arrays of the type described herein.

The RFEM 102 can be a small circuit board including a number of printedantennas and one or more RF devices containing multiple radio chains,including upconversion/downconversion 104 to millimeter wavefrequencies, power combiner/divider 106, programmable phase shifting 108and power amplifiers (PA) 110, low noise amplifiers (LNA) 112, as wellas control and power management circuitry 114 a, 114 b. This arrangementcan be different from Wi-Fi or cellular implementations, which generallyhave all RF and baseband functionality integrated into a single unit andonly antennas connected remotely via coaxial cables.

This architectural difference is driven by the very large power lossesin coaxial cables at millimeter wave frequencies. These power losseswould both reduce the transmit power at the antenna and reduce receivesensitivity. In order to avoid this issue, PA 110 and LNA 112 may bemoved to an RFEM 102 with integrated antennas. In addition, the RFEM 102may include upconversion/downconversion circuitry 104 so that the IFsignals over the coaxial cable 130 can be at a lower frequency. Thesystem context for mmWave 5G is discussed below.

FIG. 2 illustrates a user device 200, according to some aspects of thepresent disclosure. The user device may be a mobile device in someaspect and, in some aspects of the present disclosure may be userequipment (UE) as that term is used in the 3rd Generation PartnershipProject (3GPP) and other communication systems. The user device 200includes an application processor 205, baseband circuitry 210, radiofront end module (RFEM) 215, memory 220, connectivity circuitry 225, NFCcontroller 230, audio driver 235, camera driver 240, touch screen 245,display driver 250, sensors 255, removable memory 260, power managementintegrated circuit (PMIC) 265, and smart battery 270.

In some aspects of the present disclosure, application processer 205 mayinclude one or more CPU cores and one or more of cache memory, lowdrop-out voltage regulators (LDOs), interrupt controllers, serialinterfaces such as SPI, I2C or universal programmable serial interfacecircuitry, real time clock (RTC), timer-counters including interval andwatchdog timers, general purpose IO, memory card controllers such asSD/MMC or similar, USB interfaces, MIPI interfaces and Joint Test AccessGroup (JTAG) test access ports.

In some aspects of the present disclosure, baseband circuitry 210 may beimplemented, for example, as a solder-down substrate including one ormore integrated circuits, a single packaged integrated circuit solderedto a main circuit board or a multi-chip module containing two or moreintegrated circuits

FIG. 3 illustrates a base station radio head 300, according to someaspects of the present disclosure. The base station radio head 300 mayinclude one or more of application processor 305, baseband circuitry310, one or more radio front end modules 315, memory 320, powermanagement circuitry 325, power tee circuitry 330, network controller335, network interface connector 340, satellite navigation receivercircuitry 345, and user interface 350.

In some aspects of the present disclosure, application processor 305 mayinclude one or more CPU cores and one or more of cache memory, lowdrop-out voltage regulators (LDOs), interrupt controllers, serialinterfaces such as SPI, I2C or universal programmable serial interfacecircuitry, real time clock (RTC), timer-counters including interval andwatchdog timers, general purpose IO, memory card controllers such asSD/MMC or similar, USB interfaces, MIPI interfaces and Joint Test AccessGroup (JTAG) test access ports.

In some aspects of the present disclosure, baseband circuitry 310 may beimplemented, for example, as a solder-down substrate including one ormore integrated circuits, a single packaged integrated circuit solderedto a main circuit board or a multi-chip module containing two or moreintegrated circuits.

In some aspects of the present disclosure, memory 320 may include one ormore of volatile memory, including dynamic random access memory (DRAM)and/or synchronous DRAM (SDRAM), and nonvolatile memory (NVM), includinghigh-speed electrically erasable memory (commonly referred to as Flashmemory), phase-change random access memory (PRAM), magneto-resistiverandom access memory (MRAM), and/or a three-dimensional crosspointmemory. Memory 320 may be implemented as one or more of solder downpackaged integrated circuits, socketed memory circuitry and plug-inmemory cards.

In some aspects of the present disclosure, power management circuitry325 may include one or more of voltage regulators, surge protectors,power alarm detection circuitry and one or more backup power sourcessuch as a battery or capacitor. Power alarm detection circuitry maydetect one or more of brown out (under-voltage) and surge (over-voltage)conditions.

In some aspects of the present disclosure, power tee circuitry 330 mayprovide for electrical power drawn from a network cable to provide bothpower supply and data connectivity to the base station radio head 300using a single cable.

In some aspects of the present disclosure, network interface circuitry335 may provide connectivity to a network using a standard networkinterface protocol such as Ethernet. Network connectivity may beprovided using a physical connection which is one of electrical(commonly referred to as copper interconnect), optical or wireless.

In some aspects of the present disclosure, satellite navigation receivercircuitry 345 may include circuitry to receive and decode signalstransmitted by one or more navigation satellite constellations such asthe global positioning system (GPS), Globalnaya NavigtsionnayaSputnikovaya Sistema (GLONASS), Galileo and/or BeiDou. The receiver 345may provide data to application processor 305 which may include one ormore of position data or time data. Time data may be used by applicationprocessor 305 to synchronize operations with other radio base stations.

In some aspects of the present disclosure, user interface 350 mayinclude one or more of buttons, such as a reset button, one or moreindicators such as LEDs and a display screen.

FIG. 4A and FIG. 4B illustrate a radio front end module (RFEM),according to some aspects of the present disclosure.

FIG. 4A illustrates an aspect of a radio front end module 400incorporating millimeter wave radio front end module (RFEM) 406 and oneor more sub-six gigahertz RFIC 416. In this aspect, the one or moresub-six gigahertz RFICs 416 may be physically separated from millimeterwave RFEM 406. In some aspects of the present disclosure RFEM 406 andone or more RFICs 416 may be in the same component. RFICs 416 mayinclude connection to one or more antennas 421. RFEM 406 may includemultiple antennas 411.

FIG. 4B illustrates an alternate aspect of a radio front end module 426.In this aspect both millimeter wave and sub-six gigahertz radiofunctions may be implemented in the same physical radio front end module431. RFEM 431 may incorporate both millimeter wave antennas 436 andsub-six gigahertz antennas 441.

FIG. 5 illustrates a multi-protocol baseband processor 500, according tosome aspects of the present disclosure.

Baseband processor 500 may include one or more of IF interface 505,analog IF subsystem 510, downconverter and upconverter subsystem 520,frequency synthesizer 525, analog baseband subsystem 530, data convertersubsystem 535 and 5G digital baseband 540. Baseband processor 500 mayalso include one or more of 4G digital baseband subsystem 545, 3Gdigital baseband subsystem 550, 2G digital baseband subsystem 555 anddigital IQ interface subsystem 560.

In some aspects of the present disclosure, digital baseband subsystemswhich may include one or more of 540, 545, 550 and 555 may be coupledvia interconnect subsystem 565 to one or more of CPU subsystem 570,audio subsystem 575 and interface subsystem 580. Interconnect subsystem565 may include one or more buses and/or one or more network-on-chip(NOC) structures.

FIG. 4C illustrates an example of a system for generating multicarrierbaseband signals for transmission according to some aspects of thepresent disclosure. In an aspect, data 430 may be input to an encoder432 to generate encoded data 435. Encoder 432 may include a combinationof one or more of error detecting error correcting rate matching andinterleaving Encoder 432 may further include a step of scrambling. In anaspect, encoded data 435 may be input to a modulation mapper 405 togenerate complex valued modulation symbols 440. Modulation mapper maymap groups containing one or more binary digits, selected from encodeddata 435, to complex valued modulation symbols according to one or moremapping tables.

In an aspect, complex-valued modulation symbols 440 may be input tolayer mapper 410 to be mapped to one or more layer mapped modulationsymbol streams 445. Representing a stream of modulation symbols 440 asd(i) where i represents a sequence number index, and the one or morestreams of layer mapped symbols as x(k)(i) where k represents a streamnumber index and i represents a sequence number index, the layer mappingfunction for a single layer may be expressed as:x ⁽⁰⁾(i)=d(i)  (1)and the layer mapping for two layers may be expressed as:x ⁽⁰⁾(i)=d(2i)  (2)x ⁽¹⁾(i)=d(2i+1)  (3)Layer mapping may be similarly represented for more than two layers.

In an aspect, one or more streams of layer mapped symbols 445 may beinput to precoder 415, which generates one or more streams of precodedsymbols 450. Representing the one or more streams of layer mappedsymbols as a block of vectors:[x ⁽⁰⁾(i) . . . x ^((v-1))(i)]^(T)  (4)where i represents a sequence number index in the range 0 to M_(symb)^(layer)−1 the output is represented as a block of vectors:[z ⁽⁰⁾(i) . . . z ^((P-1))(i)]^(T)  (5)where i represents a sequence number index in the range 0 to M_(symb)^(ap)−1. The precoding operation may be configured to include one ofdirect mapping using a single antenna port, transmit diversity usingspace-time block coding or spatial multiplexing

In an aspect, each stream of precoded symbols 450/450A may be input to aresource mapper 420/420A, which generates a stream of resource mappedsymbols 455/455A. The resource mapper 450/450A may map precoded symbolsto frequency domain subcarriers and time domain symbols according to amapping which may include contiguous block mapping randomized mapping orsparse mapping according to a mapping code.

In an aspect, the resource mapped symbols 455/455A may be input tomulticarrier generator 425/425A, which generates time domain basebandsymbol 460/460A. Multicarrier generator may generate time domain symbolsusing for example, an inverse discrete Fourier transform (DFT), commonlyimplemented as an inverse fast Fourier transform (FFT) or a filter bankcomprising one or more filters.

In an aspect, where resource mapped symbols 455 are represented ass_(k)(i), where k is a subcarrier index and i is a symbol number index,a time domain complex baseband symbol x(t) may be represented as:x(t)=Σ_(k) s _(k)(i)p _(T)(t−T _(sym))exp[j2πf _(k)(t−T_(sym)−τ_(k))]  (6)Where p_(T)(t) is a prototype filter function, T_(symb) is the starttime of the symbol period, □ is a subcarrier dependent time offset, andf_(k) is the frequency of subcarrier k. Prototype functions p_(T)(t) maybe, for example, rectangular time domain pulses, Gaussian time domainpulses or any other suitable function.

FIGS. 6A, 6B and 6C illustrate frame formats that may be used in variousaspects.

FIG. 6A illustrates a periodic radio frame structure 600 that may beused in various aspects. Radio frame structure 600 has a predeterminedduration and repeats in a periodic manner with a repetition intervalequal to the predetermined duration. Radio frame 600 is divided into twoor more subframes 605. In an aspect, subframes may be of predeterminedduration which may be unequal. In an alternative aspect, subframes maybe of a duration which is determined dynamically and varies betweensubsequent repetitions of radio frame 600.

FIG. 6B illustrates an aspect of a periodic radio frame structure usingfrequency division duplexing (FDD). In an aspect of FDD, downlink radioframe structure 610 is transmitted by a base station to one or mobiledevices, and uplink radio frame structure 620 is transmitted by acombination of one or more mobile devices to a base station.

FIGS. 7A, 7B and 7C illustrate examples of constellation designs of asingle carrier modulation scheme that may be transmitted or received byan aspect.

Constellation points 7XX, where XX indicates distinguishing numerals,are shown on orthogonal in-phase and quadrature (IQ) axes, representingrespectively, amplitudes of sinusoids at the carrier frequency andseparated in phase from one another by 90 degrees.

FIG. 7A represents a constellation containing 2 points 700A, 720A, knownas binary phase shift keying (BPSK). FIG. 7B represents a constellationcontaining 4 points (two of which are enumerated as 720B, 700B) known asquadrature phase shift keying (QPSK). FIG. 7C represents a constellationcontaining 16 points 700, known as quadrature amplitude modulation (QAM)with 16 points (16QAM or QAM16). Higher order modulation constellations,containing for example 64, 256 or 1024 points may be similarlyconstructed.

In the constellations depicted in FIGS. 7A, 7B and 7C, binary codes720A, 720B and 720C are assigned to the points 700A, 700B and 700C ofthe constellation using a scheme such that nearest-neighbor points, thatis, pairs of points separated from each other by the minimum Euclidiandistance, have an assigned binary code 720A, 720B 720C differing by onlyone binary digit. For example, in FIG. 7C, the point assigned code 1000has nearest neighbor points assigned codes 1001, 0000, 1100 and 1010,each of which differs from 1000 by only one bit.

FIGS. 8A and 8B illustrate examples of alternate constellation designsof a single carrier modulation scheme that may be transmitted andreceived by some aspects of the present disclosure.

The next generation communication systems can utilize large antennaarrays for mmWave communication. Due to small wavelength, large numbersof RFFEs will be packed in a very small area to have the beamforminggain needed to compensate high path loss. However, one critical issuewith mmWave systems is thermal management (sometimes referred to asthermal mitigation) of RFFE components. In general, the power efficiencyof RFFE components decreases with operating frequency, which willgenerate a lot of excessive energy, and performance of these componentsdepends on their temperature. In general heat sinks are used to transferthe heat out of the RFFE. However, when the small size of mmWave RFFEare considered, i) the performance of form factor appropriate thermalmitigations may be insufficient to keep the RFFE operating at optimaltemperatures, and ii) distribution of heat over the RFEM can be uneven.

A previous solution to the thermal distribution problem is core hoppingWith core hopping an RFIC can be powered off for a short duration. Inother words, in standard core hopping a subset of antennas or RFICs isactive for transmissions and a subset is changing over time. However,frames sent during that duration have a significantly degraded beam,e.g., the beam width will be wider, the main lobe gain will be somewhatless, and the side lobe levels could be significantly worse. The corehopping approach would be especially inferior for broad beams, which maybe heavily utilized during the beam refinement phase (BRP) and sectorsweeps, because the pseudo-omni code word is very sensitive to whichelements/quads/RFICs are active. This is because theelements/quads/RFICs are usually covering different angular targets,which is not the same as with a very narrow beam. On the other hand, thedisclosed subject matter focuses on identifying multiple codebook codewords that switch off selected RFFEs but remain other RFFEs active witha result that approaches, and in some aspects even surpasses, the beamquality (per the metrics above), versus having all antenna elementsactive. In particular, the system can cycle (or iterate) through thegood alternatives to all elements active in a manner that reduces theduty cycle on a per array quad or per array element basis, depending onthe limitations of the RFIC, so as to reduce spatial hotspots in theRFIC. The terms RFIC and RFFE may be used herein to mean the sameelement or component. The codebook referred to above can be consideredan RFFE thinning codebook as compared to a beamforming codebook.

The disclosed subject matter responds to real-time thermal measurementsto select the code words that will provide the most desirable coolingfor the current hotspot locations. In short, an algorithmic method isdisclosed to design a codebook which reduces the total number of activeRFFEs used at a time, while reducing side lobe levels of the arraypattern, is disclosed. Then, the designed codebook is used to switch offa subset of RFFEs over time without affecting performance of theexisting beamforming codebook. An example RFFE selection scheme is shownin FIG. 9, discussed below. The algorithm for a TX/RX chain selectionscheme that is created reduces spatial thermal density, where the term“Tx/RX chain” is understood to mean a complete path through atransmitter and transmit/receive antennas and finally through areceiver. This also enables low power mmWave systems by turning off theentire TX/RX chain including power amplifier (PA), low noise amplifier(LNA), phase shifters, and other active components. This enables smallform factor RFFE design. In some aspects of the present disclosure, theheat sink can perhaps be removed completely.

In the disclosed subject matter, code words are determined that for avery specific beam are the most nearly optimal to reproduce all-elementscode word beam performance, by assembling a set of antenna thinning codewords that can allow every quad (or element) to be idle for aconfigurable duration. This means determining a diverse set of codewords for the given beam, that results in an adaptive or flexiblecapability to dial up or down the degree of thinning thus reducing theduty cycle of hotspots. Stated another way the method responds toreal-time thermal measurements to choose the code words that willprovide nearly or essentially the best cooling for the current hotspotlocations.

Further, previous solutions do not have stable beam shaping because theyexperience different effective channels when switching over code wordsof a codebook. However, maintaining a fixed beam pattern for seamlessswitching over the code words of codebook is desirable. This desirableresult is achieved by the code word switching and RFIC rotationdisclosed, which is practically transparent from a receiver perspective.Further still, previous solutions do not guarantee a desirable beampattern in terms of side lobe level, beam width, beam gain and relatedparameters after turning off a subset of RFICs. However, a switchinginterval for executing the disclosed code words is slower, as comparedto standard core hopping and therefore keeps the communication channelvirtually fixed from the receiver point of view, which is desirable.Finally, previous solutions do not respond to real-time thermalmeasurements to choose the code words that will provide the best coolingfor the current hotspot locations.

As yet another advantage, disclosed simple switching over of antennasimproves beam forming by a specific binary optimization method, which isadapted to obtain a specific beam with reduced side lobes, and with adesirable beam gin, thus providing stable beam pattern shaping with highor nearly maximum, diversity.

FIG. 9 illustrates an antenna array system with a smart RFFE selectionsequence to distribute heat, or thermal density, over the antenna array,according to some aspects of the present disclosure. FIG. 9 represents kiterations (or selections) 900 of turning RFFEs on and off by code word,where k=1, . . . , K. In FIG. 9, K is 3. At 901, 903, 905, the clearsquares represent RFFEs that are turned on and the cross-hatched squaresrepresent RFFEs that are switched off by a code word. At 901, selection1 in the sequence of 1, . . . , k, . . . , K, the cross-hatched squaresrepresent RFFEs that by real-time thermal measurement are found, at thetime of selection 1, to require thermal management (sometimes referredto as thermal mitigation) and are switched off by the code words, thatare generated by the algorithms discussed below. At 903, selection k inthe sequence of 1, . . . , k, . . . , K, the cross-hatched squaresrepresent RFFEs that are found by real-time thermal measurement at thetime of selection k to require thermal management and are switched offby the algorithm. At 905, selection K in the sequence of 1, . . . , k, .. . , K, the cross-hatched squares represent RFFEs that are found byreal-time thermal measurement at the time of selection k to requirethermal management and are switched off by the algorithm. Thisillustrates sequencing the switching of RFFEs off by iteration of codewords based on real-time thermal measurement in the RFFEs.

FIG. 9A is a diagram 906 of hardware configured to physically measuretemperature at one more locations within each RFIC, according to someaspects of the disclosure. The below-described thermal measurementimplementation may be a physical part of a wireless mobile communicationdevice itself. Modem 907 may be coupled to a plurality of RFICs. Modem907 is coupled to RFIC1 1909 by line 908, to RFIC2 911 by line 910, andto RFICn 913 by line 912, where lines 908, 910 and 912 are coupled to acontrol communications interface between modem 907 and the RFICs,according to some aspects of the disclosure. In the disclosedimplementation, baseband modem 907 interrogates the current temperaturefrom one or more RFICs 909, 911, 913, . . . , which may be accomplishedby a command sent over the control communications interface which, insome aspects could be over a Manchester encoded 300 MHz control channel.With respect to RFIC 909, a first step may be for modem 907 to send atemperature read command, which may be entitled “TEMP” to either asingle RFIC 909, or, in some aspects, broadcast to all RFICs 909, 911, .. . , 913. The RFIC to which the TEMP command is sent may sampletemperature using thermal sensors at one or more locations within theRFIC, such as, in some aspects, per feed to the antenna array that iscoupled to the RFIC, thus leveraging the integrated circuitry of theRFICs as indicated at 909A, 911A, . . . , 913A, which illustrates the“per feed to the antenna array.” However, the thermal sensors could belocated elsewhere in an RFIC, as needed. In some aspects the thermalsensors are distributed within the RFIC of the RFFE, per quad of antennaelements, and the control communication is sent from the baseband modemto the corresponding RFIC in order to interrogate the temperature asdiscussed above.

In a second step the RFIC(s) return the current temperature to basebandmodem 907. At step 3, firmware running on the modem 907 may leverage thecurrent temperature measurements at the various special locations withinthe RFIC. This may be implemented for each of the subsystems of anantenna array, according to some aspects of the disclosure. Thetemperature measurements are used to determine the weight fed to analgorithm that selects the desired duty cycle of the circuitry thatfeeds each antenna element in the array, as discussed above in thisparagraph.

The key concept is that each code word candidate has a particular dutycycle profile based on the elements that are not used for the beam, orare used at a lower power level. The objective is to select/schedulethose one or more code words such that the low duty cycle of specificelements corresponds to the measured high temperature of the circuitrysupporting those elements. In additional detail, algorithms implementedon the modem or other processing elements leverage the temperaturemeasurements received from different spatial regions within one or moreRFICs such as per LNA/PA/phase shifters/switch feeding each element orsubarray within the array. The objective of these algorithms is toidentify and mitigate hotspots within the one or more RFICs feeding theantenna array. The temperature measurements are used to determinewhether specific portions of the system are operating at sufficientlyhigh temperature levels which could impact performance. A desired dutycycle of operation for each spatial region can be determined based onthese temperature measurements with hotter regions being identified tooperate at a lower duty cycle until the operating temperature in theseregions is brought down to the desired temperature. Using thisinformation about the current hotspots and the desired duty cycle tomitigate these hotspots, codewords of a thinning code book can beselected which in aggregate achieve the desired duty cycle of operationin the identified hot spatial regions. This is accomplished since eachof the interchangeable code words offer similar beams but with differentsets of elements idle or operating at a lower transmit power. Thus, thescheduling of the appropriate code words effectively reduces the dutycycle of operation of the circuitry within the hotspots identified tomeet the desired duty cycle, and results in a reduction of heat in thesehotspots.

FIG. 10 illustrates a uniform linear antenna array 1000 with twentyantenna elements. The algorithm that controls the switching of FIG. 9 isexplained with respect to the uniform linear antenna array shown in FIG.10, and can be then extended to rectangular antenna arrays. An indicatorvector for TX/RX chain selection can be denoted by d_(i)=[d₀, d₁, . . ., d_(N)], where N is the total number of RFFEs such that d_(i)∈{0,1},i=0, . . . , N. Here, in {0, 1} means a TX/RX chain is turned off and 1means a TX/RX chain is turned on. Next, the problem can be formulatedsuch that M RFFEs out of N RFFEs are selected, (where M<N), such thatthe side lobes are reduced while maintaining the similar beamforminggain 20 log₁₀ M. Accordingly, l∞-norm minimization, can be used toreduce side lobe levels. This means minimizing the maximum values of theindividual elements of vector F(0)Ad in Equation (7), below, where eachelement of vector F(0)Ad represents array gain over side lobe, andminimizing the maximum values represents minimizing the side lobes. Thishas been discussed in the paper C. Rusu, N. González-Prelcic and R. W.Heath, “Antenna array thinning for antenna selection in millimeter waveMIMO systems,”2016 IEEE International Conference on Acoustics, Speechand Signal Processing (ICASSP), Shanghai, 2016, pp. 3416-3420.Therefore, the problem can be formulated as follows:

$\begin{matrix}{\min\limits_{{d_{i} \in {\{{0,1}\}}},{{\sum\limits_{i}d_{i}} = M}}{{{F(\theta)}{Ad}}}_{\infty}} & (7)\end{matrix}$Where F(θ)Ad is a vector and the illustrated function is a diagonalmatrix of antenna pattern f(Θ_(k)), k=1, . . . , K, and the minimizationis minimizing the elements of the vector, which represents minimizingthe side lobes. The matrix A∈C^(K×N) is given by the set of vectorscorresponding to azimuth angles located at the side lobes as follows:

$\begin{matrix}{A = {\begin{bmatrix}a_{1}^{T} \\\vdots \\a_{k}^{T} \\\vdots \\a_{K}^{T}\end{bmatrix} = \begin{bmatrix}1 & e^{j\frac{2\pi}{\lambda}d_{a}{\cos{(\theta_{1})}}} & \cdots & e^{j\frac{2\pi}{\lambda}{d_{a}{({N - 1})}}{\cos{(\theta_{1})}}} \\\vdots & \vdots & \vdots & \vdots \\1 & e^{j\frac{2\pi}{\lambda}d_{a}{\cos{(\theta_{k})}}} & \cdots & e^{j\frac{2\pi}{\lambda}{d_{a}{({N - 1})}}{\cos{(\theta_{k})}}} \\\vdots & \vdots & \vdots & \vdots \\1 & e^{j\frac{2\pi}{\lambda}d_{a}{\cos{(\theta_{K})}}} & \cdots & e^{j\frac{2\pi}{\lambda}{d_{a}{({N - 1})}}{\cos{(\theta_{K})}}}\end{bmatrix}}} & (8)\end{matrix}$

-   -   where    -   d_(a) is inter-radiator element distance for a uniform linear        antenna array in terms of wavelength λ;    -   a is the array response vector for the angle of arrival or angle        of departure, Θ_(k), and T is a transpose operator.        Defining the matrix A on the antenna pattern F(Θ) keeps the        maximum side lobe levels to a minimum.

The above is a binary l∞-norm minimization problem which means that itis a non-convex and NP-hard problem. Therefore, a weighted convexrelaxation technique can be used, as shown, e.g., in the above-citedpaper C. Rusu, N. González-Prelcic and R. W. Heath, or in the paper, B.Fuchs, “Synthesis of Sparse Arrays With Focused or Shaped Beam patternvia Sequential Convex Optimizations,” in IEEE Transactions on Antennasand Propagation, vol. 60, no. 7, pp. 3499-3503, July 2012. These twopapers are two examples among many. In this disclosure, we will use atechnique which adds a penalty to an objective function such that normmaximization is achieved for binary variables b_(i).

$\begin{matrix}{{\min\limits_{{b_{i} \in {\lbrack{0,1}\rbrack}},{{\sum\limits_{i}d_{i}} = M}}{{{F(\theta)}{Ad}}}_{\infty}} + \frac{w^{H}b}{M}} & (9)\end{matrix}$

where b_(i) is relaxation of d_(i). In the original problem formulationin (7), d_(i) was either 0 or 1. In equation (9), we replace d_(i) withb_(i) such that b_(i) can be a real number between 0 and 1, i.e.,b_(i)∈[0,1]. In equation (9), the second term is relaxation term forweighted optimization of b_(i) for faster convergence. The weight isgiven by vector w.

A method to determine a set of TX/RX chain selection vectors, namely acodebook, such that a desired thermal density is achieved, will now bedescribed. The designed codebook can account for the expected orreal-time measured thermal buildup throughout the antenna array, asdiscussed above, for the purposes of statistically shifting which codewords are selected, thus improving the ability of the system to adapt tohotspots in the system and to therefore minimize the peak spatialthermal density during operation, while maximizing beam quality. Inrespect of expected thermal buildup, if the thermal buildup ispredictable, the codebook can be designed offline.

Codebook Design for TX/RX Chain Selection

One step of the method is the determination of the selection of thenumber of active TX/RX chains, M, out of N TX/RX chains where M TX/RXchains are required to maintain the desired beam forming gin of 10 log10(M). Since operating a fewer number of antennas means less radiatedpower, assuming that each TX chain has its own power amplifier, and lesscombining gin for the RX chain, the total number of active TX/RX chainsshould be selected such that the communication link has enoughbeamforming gin, i.e., the desired beamforming gain≤20 log 10 M. Turningoff N-M TX/RX chains will save roughly (N−M)/N % of the power at theRFIC. In addition, the M should be selected considering the tradeoffs ofsignal to noise ratio (SNR) limitations, spatial thermal overload, andinterference risk, meaning victim and/or aggressor. SNR limitation isupper bounded by 20 log₁₀ M. The purpose of the propose algorithm isthermal density reduction at the antenna array. Thermal densityreduction is achieved by turning off some of the RFFE elements.Therefore, reducing thermal overload can decrease SNR gain due todecrease at the beamforming gain, but the disclosed code word basedantenna thinning keeps the SNR decrease to a minimum, which may beconsidered a side benefit of the described optimization. Sub-optimalRFFE switching antenna elements off may increase beam width andside-lobe level. This may increase interference. The proposed solution(optimized RFFE switching by code word-based antenna thinning), on theother hand, minimizes increase in beam width and in side lobe level, andminimizes interference increase, and therefore represents significantimprovements over other methods. Further, turning off RFFEs results inloss of beam forming gin. However, the described optimization results inthe loss of beam forming gin being minimal compared to other solutions,such as modular antenna switching as shown by simulated resultsdiscussed below.

A second step in creating the codebook is to iteratively design codewords for the codebook. Since the codebook is designed such that goodthermal density is achieved, some of the TX/RX chains can be preselectedthat have to be turned off, and then find the remaining TX/RX chainsthat can be switched off to have essentially the lowest side lobe level,and that results in the required number of TX/RX chains to be turnedoff. Subarray type RFFE selection is a special case of the suggestedalgorithm such that preselection of M TX/RX chains out of N TX/RX chainson a modular basis may occur (use of one half or one fourth of array ata time etc.). The special case is switching off contiguous subsets ofRFFEs as shown in FIG. 10A. FIG. 10A illustrates both subarray selectionand codebook antenna thinning according to some aspects of the presentdisclosure. Subarray selection is not optimized and is represented withrespect to array 1001. Array element groups 1001A, 1001B, 1001C and1001D are subarrays of 4×4 elements of an 8×8 array. Subarray selectioncan be used as an approach to thermal mitigation without anyoptimization where subarrays may be switched, for example, from 1001A,to 1001B, 1001C to 1001D. Since antenna arrays are designed in modularfashion, i.e., small antenna arrays are put together to have a largerantenna array, turning off subarrays can be considered as a thermalmitigation solution but it is sub-optimal and results in growth of sidelobes and growth of beam width, neither of which is desirable. Incodebook-based antenna thinning antenna elements are turned on and offaccording to a codebook, where in the antenna array 1003, antenna arrayelements are selected to be turned off according to code words whichresults in on/off patterns, parts of which are seen in 1003A, 1003B,1003C and 1003D. As compared to subarray selection, the disclosedcodebook-based antenna thinning results in binary (on/off) optimization,or improvement, wherein the beam width is maintained and the side lobesare lower. The algorithms used for codebook design are discussed hereinbelow.

Algorithm-1 (Selects which ones of the M RFFEs are to be off for onecode word in the codebook.) Input: w⁽⁰⁾ = 1_(N), where 1_(N) is vectorof 1 of size N, M is the number of RFFEs that need to be turned off M, dis set to a binary vector with preselected elements that are zero,iteration number K, Z = {1 , . . . , N}. Set Z

Z\m, m is the index of zero element in vector of d which is an auxiliaryvector to keep track of index of turned on and turned off RFFEs. b

d  while |Z|>M   For K iterations    • Solve (10)     ${\min\limits_{{b_{i} \in {\lbrack{0,1}\rbrack}},\;{{\sum_{i}b_{i}} = M},\mspace{11mu}{i \in \mathcal{Z}}}\mspace{59mu}{{{F(\theta)}{Ab}}}_{\infty}} + \frac{w^{H}b}{M}$   • Update w_(i) ← 1 − b_(i), i ∈  

  End   ${\bullet\mspace{14mu} m} = {\arg\;{\underset{i}{\mspace{11mu}\min}\mspace{14mu} b_{i}}}$  •

 ←

\m, d_(m) = 0.   End

-   -   The codebook may then be designed for good thermal density by a        second algorithm:

Algorithm-2 Input: The set of essential TX/RX chains for theimaldistribution that is switched off at the time the thermal measurement ismade,

 = 0. while d_(i) = 0, ∀i ∈ {1, . . . , N} ∀d ∈

, where

 is the codebook. Select some indexes i such that d_(i) ≠ 0, ∀i ∈ {1, .. . , N} ∀d ∈

, solve Algorithm-1

 ←

 U d End

FIG. 11 illustrates an example 1100 of TX/RX selection for thermaldensity, according to some aspects of the present disclosure.Performance for an N=8×8, or 64, element rectangular array will bediscussed. Consider M=32. This means that there is about 50% less powerdissipation at the RF front end. The codebook is given by the symbol

. for FIG. 11, seen at 1100 are two codewords 1102, 1104 that have beengenerated for TX/RX chain selection. In one aspect of the disclosure, inorder to cover all codewords, 9 codewords are generated to be able toturn-off each RFFE at least once. This means that some antenna elementscan be turned off more than once to get a desired beam pattern for allcodewords. The codeword-based antenna thinning in this case wassimulated and when compared with subarray type TX/RX chain selection inwhich only half of the (8×4) or 32 array is activated to have the samenumber of active elements (i.e., 32), the codeword-based thermalmitigation actually increased the main lobe by about 0.35 dB whiledecreasing the side lobes by 7.1 dB.

FIG. 12 illustrates at 1200 a comparison of simulated array patterns ofan antenna array using the disclosed thermal mitigation with arraypatterns of subarray type TX/RX chain selection, according to someaspects of the present disclosure. In FIG. 12, only half of the (4×8)array is activated to have the same number of active elements, i.e., 32.Curve 1310 is array gin with the disclosed codeword-based thermalmitigation and curve 1320 illustrates array in with subarray-typethermal mitigation. Comparison of the two curves illustrates that thereis essentially no loss at main beam power which is 20 log₁₀ M=20 log₁₀32=30.1030 dB. This means that switching RFFE elements according to thedisclosed thermal mitigation method will keep the existing effectivechannel to maintain the beam pattern as similar as possible when anantenna element is switched from an “on” condition to an “off”condition.

FIG. 13 illustrates at 1300 a comparison of side lobe levels (SLL) withsimulated antenna array operation in accordance with the presentdisclosure, and operation of simple subantenna array type TX/RXselection, according to some aspects of the present disclosure. Curve1410 represents the side lobe level with the disclosed thermalmitigation method used and curve 1420 represents the side lobe levelusing subarray-based TX/RX chain selection. The side lobe levels (SLL)of the proposed codebook operation can be seen by observation to besignificantly lower than with subarray type TX/RX selection. Thehorizontal axis in FIG. 13 represents indexes of codewords that aregenerated for the example 1200 of TX/RX selection in FIG. 12.

FIG. 14 illustrates at 1500 a comparison of antenna array gain as afunction of azimuth when all antennas are operated, and antenna arraygain when the antenna array is operated with the disclosed thermalmitigation method, according to some aspects of the present disclosure.FIG. 14 was achieved using simulation. Curve 1510 illustrates the arraygain using the disclosed thermal mitigation, and curve 1520 illustratesthe array actor with all antennas used. By observation it can be seenthat the case when all the TX/RX chains are used for beamforming versusthe case of using half the antennas results in a difference at maximumbeamforming gain is approximately 6 dB. The SLL is about 1 dB lower thanthe case in which all the TX/RX chains are used. In this case beam widthwas similar while the side lobes were reduced. The comparison is atwo-dimensional plot. A simulated three-dimensional plot illustrates thesame comparison result.

FIG. 15 is a flow chart that illustrates a method 1500, according tosome aspects of the present disclosure. At 1501 the method begins with NTX/RX chains. At 1503 the Number M is selected, where M is less than N.M is selected to satisfy the desired beamforming gain, 10 log 10(M). Mis also selected to satisfy SNR limitations and to reduce side lobelevels. M is also selected to have the desired thermal reduction andsufficient power dissipation reduction. At 1505, ones of the M TX/RXchains are preselected for turn-off, depending on system constraints. At1507, ones of the TX/RX chains are preselected such that subarrays areturned off. At 1509 Matrix A is defined to reduce side lobes. At 1511,an iteration number K is defined for the desired beam pattern. At 1513,the codebook is designed algorithmically, based on Algorithm 1 andAlgorithm 2 discussed above, by taking into account the antenna patternfor better performance based on side lobe reduction.

FIG. 16 illustrates a block diagram of an example machine 1600 uponwhich any one or more of the techniques or methodologies discussedherein may be performed, according to some aspects of the presentdisclosure. In alternative aspects, the machine 1600 may operate as astandalone device or may be connected (e.g., networked) to othermachines. In a networked deployment, the machine 1600 may operate in thecapacity of a server machine, a client machine, or both in server-clientnetwork environments. In an example, the machine 1600 may act as a peermachine in peer-to-peer (P2P) (or other distributed) networkenvironment. The machine 1600 may be a UE, eNodeB, AP, STA, personalcomputer (PC), a tablet PC, a set-top box (STB), a personal distalassistant (PDA), a mobile telephone, a smart phone, a web appliance, anetwork router, switch or bridge, or any machine capable of executinginstructions (sequential or otherwise) that specify actions to betakenby that machine. Further, while only a single machine is illustrated,the term “machine” shall also be taken to include any collection ofmachines that individually or jointly execute a set (or multiple sets)of instructions to perform any one or more of the methodologiesdiscussed herein, such as cloud computing software as a service (SaaS),other computer cluster configurations.

Examples, as described herein, may include, or may operate on, logic ora number of components, circuitry, modules or mechanisms. Circuitry is atangible entity (e.g., hardware) capable of performing specifiedoperations and may be configured or arranged in a certain manner. In anexample, circuits may be arranged (e.g., internally or with respect toexternal entities such as other circuits) in a specified manner, in someaspects as a module. In an example, the whole or part of one or morecomputer systems (e.g., a standalone, client or server computer system)or one or more hardware processors may be configured by firmware orsoftware (e.g., instructions, an application portion, or an application)as a module that operates to perform specified operations. In anexample, the software may reside on a machine readable medium. In anexample, the software, when executed by the underlying hardware of themodule, causes the hardware to perform the specified operations.

Accordingly, the term “circuitry” is understood to encompass a tangibleentity, be that an entity that is physically constructed, specificallyconfigured (e.g., hardwired), or temporarily (e.g., transitorily)configured (e.g., programmed) to operate in a specified manner or toperform part or all of any operation described herein. Consideringexamples in which modules or circuitry are temporarily configured, eachof the modules or circuitry need not be instantiated at any one momentin time. For example, where the circuitry comprise a general-purposehardware processor configured using software, the general-purposehardware processor may be configured as respective different modules ordifferent circuitry at different times. Software may accordinglyconfigure a hardware processor, for example, to constitute a particularmodule at one instance of time and to constitute a different module at adifferent instance of time.

Machine (e.g., computer system) may include a hardware processor 1602(e.g., a central processing unit (CPU), a graphics processing unit(GPU), a hardware processor core, or any combination thereof), a mainmemory 1604 and a static memory 1606, some or all of which maycommunicate with each other via an interlink (e.g., bus) 1608. Themachine 1600 may further include a display unit 1610, an alphanumericinput device 1612 (e.g., a keyboard), and a user interface (UI)navigation device 1614 (e.g., a mouse). In an example, the display unit1610, input device 1612 and UI navigation device 1614 may be a touchscreen display. The machine 1600 may additionally include a storagedevice (e.g., drive unit) 1616, a signal generation device 1618 (e.g., aspeaker), a network interface device 1620, and one or more sensors, suchas a global positioning system (GPS) sensor, compass, accelerometer, orother sensor. The machine 1600 may include an output controller 1628,such as a serial (e.g., universal serial bus (USB), parallel, or otherwired or wireless (e.g., infrared (IR), near field communication (NFC),and the like.) connection to communicate or control one or moreperipheral devices (e.g., a printer, card reader, and the like).

The storage device 1616 may include a machine readable medium 1622 onwhich is stored one or more sets of data structures or instructions 1624(e.g., software) embodying or utilized by any one or more of thetechniques or functions described herein. The instructions 1624 may alsoreside, completely or at least partially, within the main memory 1604,within static memory 1606, or within the hardware processor 1602 duringexecution thereof by the machine. In an example, one or any combinationof the hardware processor 1602, the main memory 1604, the static memory1606, or the storage device 1616 may constitute machine readable media.

While the machine readable medium 1622 is illustrated as a singlemedium, the term “machine readable medium” may include a single mediumor multiple media (e.g., a centralized or distributed database, and/orassociated caches and servers) configured to store the one or moreinstructions 1624.

The term “machine readable medium” may include any medium that iscapable of storing encoding or carrying instructions for execution bythe machine and that cause the machine to perform any one or more of thetechniques of the present disclosure, or that is cap able of storingencoding or carrying data structures used by or associated with suchinstructions. Non-limiting machine readable medium examples may includesolid-state memories, and optical and magnetic media. Specific examplesof machine readable media may include: nonvolatile memory, such assemiconductor memory devices (e.g., Electrically Programmable Read-OnlyMemory (EPROM), Electrically Erasable Programmable Read-Only Memory(EEPROM)) and flash memory devices; magnetic disks, such as internalhard disks and removable disks; magneto-optical disks; Random AccessMemory (RAM); and CD-ROM and DVD-ROM disks. In some examples, machinereadable media may include non-transitory machine readable media. Insome examples, machine readable media may include machine readable mediathat is not a transitory propagating signal.

The instructions 1624 may further be transmitted or received over acommunications network 1626 using a transmission medium via the networkinterface device 1620 utilizing any one of a number of transferprotocols (e.g., frame relay, internet protocol (IP), transmissioncontrol protocol (TCP), user datagram protocol (UDP), hypertext transferprotocol (HTTP), and the like). Example communication networks mayinclude a local area network (LAN), a wide area network (WAN), a packetdata network (e.g., the Internet), mobile telephone networks (e.g.,cellular networks), Plain Old Telephone (POTS) networks, and wirelessdata networks (e.g., Institute of Electrical and Electronics Engineers(IEEE) 802.11 family of standards known as Wi-Fi®, IEEE 802.16 family ofstandards known as WiMax®), IEEE 802.15.4 family of standards, a LongTerm Evolution (LTE) family of standards, a Universal MobileTelecommunications System (UMTS) family of standards, peer-to-peer (P2P)networks, among others. In an example, the network interface device 1620may include one or more physical jacks (e.g., Ethernet, coaxial, orphone jacks) or one or more antennas to connect to the communicationsnetwork 1626. In an example, the network interface device 1620 mayinclude a plurality of antennas to wirelessly communicate using at leastone of single-input multiple-output (SIMO), multiple-inputmultiple-output (MIMO), or multiple-input single-output (MISO)techniques. In some examples, the network interface device 1620 maywirelessly communicate using Multiple User MIMO techniques. The term“transmission medium” shall be taken to include any intangible mediumthat is capable of storing encoding or carrying instructions forexecution by the machine, and includes digital or analog communicationssignals or other intangible medium to facilitate communication of suchsoftware.

EXAMPLES

Example 1 is an apparatus for a User Equipment (UE), the apparatuscomprising N transmit/receive (TX/RX) chains, each TX/RX chaincomprising an RFFE, each RFFE comprising one or more thermal sensorsconfigured to measure heat in the RFFE; an antenna array coupled to theplurality of TX/RX chains; and a codebook comprising a plurality of codewords configured to respond to real-time heat measurements from thethermal sensors in each TX/RX chain to switch off selected TX/RX chainsto reduce thermal density at the antenna array.

In Example 2, the subject matter of Example 1 optionally includeswherein the magnitude of the side lobe levels of the antenna array isreduced after the selected TX/RX chains are switched off.

In Example 3, the subject matter of any one or more of Examples 1-2optionally include wherein a beamforming gin of the antenna array issubstantially the same after the selected TX/RX chains are switched offas the antenna array beamforming gain before the selected TX/RX chainsare switched off.

In Example 4, the subject matter of any one or more of Examples 1-3optionally include dB less after the selected TX/RX chains are switchedoff than the antenna array beamforming gain before the selected TX/RXchains are switched off 4 is missing parent: 5. The apparatus of Example1, wherein a communication channel received by the antenna array issubstantially the same communication channel after the selected TX/RXchains are switched off as the communication channel before the selectedTX/RX chains are switched off.

In Example 5, the subject matter of any one or more of Examples 1-4optionally include wherein a channel state indicator (CSI) valuereceived by receivers of the apparatus after the selected TX/RX chainsare switched off is substantially the same CSI value received by thereceivers of the apparatus before the selected TX/RX chains are switchedoff.

In Example 6, the subject matter of any one or more of Examples 1-5optionally include wherein information comprising the real-time heatmeasurements is sent to a modem and used to switch off the selectedTX/RX chains.

In Example 7, the subject matter of any one or more of Examples 1-6optionally include (M).

Example 8 is an apparatus of an evolved Node B (eNB), the apparatuscomprising N transmit/receive (TX/RX) chains, each TX/RX chaincomprising an, each RFFE comprising one or more thermal sensorsconfigured to measure heat in the RFFE; an antenna array coupled to theplurality of TX/RX chains; and a codebook comprising a plurality of codewords configured to respond to real-time heat measurements from thethermal sensors in each TX/RX chain to switch off selected TX/RX chainsto reduce thermal density at the antenna array.

In Example 9, the subject matter of Example 8 optionally includeswherein a magnitude of the side lobe levels of the antenna array isreduced after the selected TX/RX chains are switched off.

In Example 10, the subject matter of any one or more of Examples 8-9optionally include wherein a beamforming gain of the antenna array issubstantially the same after the selected TX/RX chains are switched offas the antenna array beamforming gin before the selected TX/RX chainsare switched off.

In Example 11, the subject matter of any one or more of Examples 8-10optionally include dB less after the selected TX/RX chains are switchedoff than the antenna array beamforming gin before the selected TX/RXchains are switched off.

In Example 12, the subject matter of any one or more of Examples 8-11optionally include wherein a communication channel received by theantenna array is substantially the same communication channel after theselected TX/RX chains are switched off as the communication channelbefore the selected TX/RX chains are switched off.

In Example 13, the subject matter of any one or more of Examples 8-12optionally include wherein a CSI value received by the receivers of theeNB after the selected TX/RX chains are switched off is substantiallythe same CSI value received by receivers of the eNB before the selectedTX/RX chains are switched off.

In Example 14, the subject matter of any one or more of Examples 8-13optionally include wherein information comprising the real-time heatmeasurements is sent to a modem and used to switch off the selectedTX/RX chains.

In Example 15, the subject matter of any one or more of Examples 8-14optionally include (M).

Example 16 is a method of designing a codebook to switch off selectedTX/RX chains to reduce thermal density in a system comprising N TX/RXchains coupled to an antenna array, wherein each TX/RX chain comprisesan RFFE, the method comprising selecting a number M of active TX/RXchains out of the N TX/RX chains, where the M TX/RX chains gives adesired system beamforming gin of 10 log 10(M), a desired system signalto noise ratio, and antenna pattern side lobe level reduction; anddesigning iterative code words for the codebook by the solution of twoalgorithms, Algorithm 1 represented by: Input: w(17 is missing parent:0)=1N, M, d is a binary vector with preselected elements that are zero,iteration number K, Z={1, . . . , N}.

Example 17 is one or more computer-readable hardware storage devicehaving embedded therein a set of instructions which, when executed byone or more processors that control N TX/RX chains, each TX/RX chaincomprising an RFFE coupled to an antenna array, each RFFE comprising oneor more thermal sensors configured to measure heat in the RFFE. theoperations comprising monitoring real-time heat measurements by the oneor more thermal sensors in each RFFE; and switching off a predeterminednumber of the N TX/RX chains by use of a codebook that comprises aplurality of code words that are configured for iterative execution byresponding to the monitored real-time heat measurements in each TX/RXchain to reduce thermal density at an antenna array coupled to the NTX/RX chains.

In Example 18, the subject matter of Example 17 optionally includeswherein the magnitude of the side lobe levels of the antenna array isreduced after the selected TX/RX chains are switched off.

In Example 19, the subject matter of any one or more of Examples 17-18optionally include wherein the antenna array beamforming gain issubstantially the same after the selected TX/RX chains are switched offas the antenna array beamforming gin before the selected TX/RX chainsare switched off.

In Example 20, the subject matter of any one or more of Examples 17-19optionally include dB less after the selected TX/RX chains are switchedoff than the antenna array beamforming gain before the selected TX/RXchains are switched off.

In Example 21, the subject matter of any one or more of Examples 17-20optionally include wherein the communication channel received by theantenna array is substantially the same communication channel after theselected TX/RX chains are switched off as the communication channelbefore the selected TX/RX chains are switched off.

In Example 22, the subject matter of any one or more of Examples 17-21optionally include wherein a CSI value received by the receivers of theapparatus after the selected TX/RX chains are switched off issubstantially the same CSI value as the CSI value received by thereceivers of the apparatus before the selected TX/RX chains are switchedoff.

In Example 23, the subject matter of any one or more of Examples 17-22optionally include wherein information comprising the real-time heatmeasurements is sent to a modem and used to switch off the selectedTX/RX chains.

In Example 24, the subject matter of any one or more of Examples 17-23optionally include wherein the code words are configured to switch offthe selected TX/RX chains while maintaining M RFFEs switched on, whereM<N and the desired beamforming gin is 10 log 10(M).

In Example 25, the subject matter can include, or can optionally becombined with any portion or combination of, any portions of any one ormore of Examples 1 through 24 to include, subject matter that caninclude means for performing any one or more of the functions ofExamples 1 through 24, or a machine-readable medium includinginstructions that, when performed by a machine, cause the machine toperform any one or more of the functions of Examples 1 through 24.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific aspects in which the disclosedsubject matter can be practiced. These aspects are also referred toherein as “examples.” In the event of inconsistent usages between thisdocument and those documents so incorporated by reference, the usage inthe incorporated reference(s) should be considered supplementary to thatof this document; for irreconcilable inconsistencies, the usage in thisdocument controls.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of“at least one” or“one or more.” In this document,the term “or” is used to refer to a nonexclusive or, such that “A or B”includes “A but not B,” “B but not A,” and “A and B,” unless otherwiseindicated. In the appended claims, the terms “including” and “in which”are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, or process that includes elements in addition to those listedafter such a term in a claim are still deemed to fall within the scopeof that claim. Moreover, in the following claims, the terms “first,”“second,” and “third,” etc. are used merely as labels, and are notintended to impose numerical requirements on their objects.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otheraspects can be used, such as by one of ordinary skill in the art uponreviewing the above description. Also, in the above DetailedDescription, various features may be grouped together to streamline thedisclosure. This should not be interpreted as intending that anunclaimed disclosed feature is essential to any claim. Rather, inventivesubject matter may lie in less than all features of a particulardisclosed aspect. Thus, the following claims are hereby incorporatedinto the Detailed Description, with each claim standing on its own as aseparate aspect. The scope of the disclosed subject matter should bedetermined with reference to the appended claims, along with the fullscope of equivalents to which such claims are entitled.

The Abstract is provided to allow the reader to ascertain the nature andgist of the technical disclosure. It is submitted with the understandingthat it will not be used to limit or interpret the scope or meaning ofthe claims. The following claims are hereby incorporated into thedetailed description, with each claim standing on its own as a separateaspect.

The invention claimed is:
 1. An apparatus comprising: a baseband modemconfigured to cause a user equipment (UE) to: receive real-timetemperature measurements from a plurality of radio frequency (RF) frontends (RFFEs) of corresponding transmit/receive (TX/RX) chains coupled toan antenna array, wherein the real-time temperature measurements arerepresentative of a respective temperature of each RFFE; identify a hotspatial region in the antenna array, based on the real-time temperaturemeasurements; and select and apply a plurality of code words from acodebook, based on the real-time temperature measurements, to controlpower of the plurality of TX/RX chains, in order to reduce thermaldensity in the hot spatial region.
 2. The apparatus of claim 1, whereinthe plurality of code words are generated using a method that minimizesa maximum of a pattern of the antenna array over one or more side lobes.3. The apparatus of claim 2, wherein the method includes weighted convexrelaxation of a binary 1-infinity norm minimization.
 4. The apparatus ofclaim 1, wherein the baseband modem is configured to switch off selectedTX/RX chains of the plurality of TX/RX chains through applying theplurality of code words.
 5. The apparatus of claim 1, wherein thecodebook is generated such that each RFFE is turned off at least oncewhen the plurality of code words is applied.
 6. The apparatus of claim1, wherein the baseband modem is configured to apply the plurality ofcode words in a cyclic fashion.
 7. The apparatus of claim 1, wherein theplurality of code words is generated to provide a stable beam patternand have, in aggregate, a desired duty cycle of operation within the hotspatial region, wherein each of the plurality of codewords has adifferent set of elements idle or operating at a lower transmit power.8. A user equipment device (UE) comprising: an antenna array; aplurality of transmit/receive (TX/RX) chains coupled to the antennaarray, each TX/RX chain of the plurality of transmit chains comprising acorresponding radio frequency (RF) front end (RFFE), each RFFEcomprising one or more thermal sensors configured to measure temperaturein the RFFE; and a baseband modem configured to: identify a hot spatialregion in the antenna array, based on real-time temperature measurementsfrom the one or more thermal sensors of each RFFE; and select and applya plurality of code words from a codebook, based on the real-timetemperature measurements, to control power of the plurality of TX/RXchains, in order to reduce thermal density in the hot spatial region. 9.The UE of claim 8, wherein the plurality of TX/RX chains includes aplurality of receivers, wherein a channel state indicator (CSI) valuereceived by the plurality of receivers prior to the plurality of codewords being applied is a same CSI value that is received by theplurality of receivers while the plurality of code words are beingapplied.
 10. The UE of claim 8, wherein the plurality of code words aregenerated using a method that minimizes a maximum of a pattern of theantenna array over one or more side lobes.
 11. The UE of claim 8,wherein the baseband modem is configured to switch off selected TX/RXchains of the plurality of TX/RX chains through applying the pluralityof code words.
 12. The UE of claim 8, wherein the plurality of TX/RXchains and the antenna array are configured transmit and receive in amillimeter-wave frequency range.
 13. The UE of claim 8, wherein eachRFFE includes two or more thermal sensors.
 14. The UE of claim 8,wherein none of the plurality of TX/RX chains includes a heat sink. 15.A non-transitory memory medium storing program instructions forexecution by one or more processors that control a plurality of TX/RXchains coupled to an antenna array, wherein the program instructions,when executed by the one or more processors, cause the one or moreprocessors to perform operations comprising: monitoring real-timetemperature measurements in each RFFE; identifying a hot spatial regionin an antenna array, based on the real-time temperature measurements;and selecting and applying a plurality of code words from a codebook,based on the real-time temperature measurements, to control power of theplurality of TX/RX chains in order to reduce thermal density in the hotspatial region.
 16. The non-transitory memory medium of claim 15,wherein the plurality of code words are generated using a method thatminimizes a maximum of a pattern of the antenna array over one or moreside lobes.
 17. The non-transitory memory medium of claim 15, wherein abeamforming gain of the antenna array is no more than 1 dB less afterthe plurality of code words have been applied than the beamforming gainof the antenna array before the plurality of code words have beenapplied.
 18. The non-transitory memory medium of claim 15, wherein theplurality of TX/RX chains includes a plurality of receivers, wherein achannel state indicator (CSI) value received by the plurality ofreceivers prior to the plurality of code words being applied is a sameCSI value that is received by the plurality of receivers while theplurality of code words are being applied.
 19. The non-transitory memorymedium of claim 15, wherein the plurality of code words is generated toprovide a stable beam pattern and have, in aggregate, a desired dutycycle of operation within the hot spatial region, wherein each of theplurality of codewords has a different set of elements idle or operatingat a lower transmit power.
 20. The non-transitory memory medium of claim15, the operations further comprising: applying the plurality of codewords in a cyclic fashion.